in the Modern Spectroscope. 105 



3. Chemical Parentage of the Spectrum under discussion. — I 

 freely admit the force of Professor Piazzi Smyth's remarks on 

 the difficulty of volatilizing carbon ; but that does not appear to 

 me to affect the experimental evidence for my assertion that " this 

 spectrum is the spectrum of carbon, and not of a hydrocarbon 

 or any other compound of carbon. >} That evidence is very 

 simple ; this spectrum can be obtained alike from compounds of 

 carbon with hydrogen, with nitrogen, with oxygen, with sulphur, 

 and with chlorine. 



Whether or not the spectrum is produced by the vapour of 

 carbon is another question ; but if this spectrum is, as Professor 

 Piazzi Smyth asserts, that of a hydrocarbon, will Professor Piazzi 

 Smyth explain how it is possible to obtain it from cyanogen, a 

 compound of carbon and nitrogen, when no hydrogen is pre 

 sent? I have just repeated the experiment with cyanogen for 

 perhaps the fiftieth time. Dry mercuric cyanide was heated in 

 a test-tube, and the gas evolved was dried by passing through a 

 tube containing phosphoric anhydride ; it then passed through a 

 tube provided with platinum wires, the end of which dipped 

 below warm and dry mercury. On passing the discharge from 

 an induction-coil between the platinum wires a spark was ob- 

 tained which gave the spectrum in question brilliantly, the gas 

 being decomposed and carbon being deposited. 



Professor Piazzi Smyth says that in May 1871, in a paper 

 sent to the Royal Astronomical Society, he " gave such extracts 

 from the authorities on either side as showed that the spectro- 

 scopists declaring for pure carbon, in opposition to those pro- 

 nouncing for carbohydrogen, were blundering little less than the 

 perpetual-motion men of last century " Permit me to quote 

 from a paper communicated by myself to the Journal of Science 

 for January 1871 : — 



" At first sight it would appear that carbon is an element un- 

 likely to yield a discontinuous spectrum, inasmuch as it is not 

 known in the gaseous condition ; and that if we obtain discon- 

 tinuous spectra from carbon compounds, they must be due to 

 some compound of carbon. Thus the bright blue lines observed 

 by Swan (1856) in the spectrum of the Bunsen-flame might be 

 supposed to be more probably due to carbonic oxide or carbonic 

 acid than to carbon itself. But we find that these same lines 

 occur not only in the spectrum of the flame, but also in the 

 spectra obtained by passing the electric spark either through 

 carbonic oxide, or olefiant gas, or cyanogen, and the lines thus 

 found to be common to compounds of carbon with different ele- 

 ments must of course be due to carbon itself. Whether they are 

 really produced by carbon in the gaseous state is a question which 

 cannot yet be certainly decided. If the carbon is in the solid 



